1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor laser diode, and more particularly, to a method for manufacturing a semiconductor laser diode in which a stable electrode is formed on the upper portion of a ridge having a narrow width by forming a passivation layer in a self-alignment method.
2. Description of the Related Art
Generally, since a laser beam generated from a laser diode has a narrow frequency width and a high directivity, the laser beam is applied in various fields such as optical communications, multiple communications, and space communications.
One of the main applications of the laser diode in the field of optical communications is in optical disc reading/recording systems. Nowadays, a laser diode having superior characteristics which can be oscillated with a low current and operated for a long time is required for compact disk players and compact disk reading/writing systems.
A conventional GaN semiconductor laser diode is manufactured by crystalizing and growing a multilayer laser structure on a sapphire substrate, and the structure has a ridge structure, wherein a p-type electrode is formed after a multilayer crystal is grown.
Particularly, as shown in FIG. 1, a buffer layer 4, a first clad layer 6, a first waveguide layer 8, an active layer 10, a second waver layer 12, a second clad layer 14, and a cap layer 16 are sequentially formed on a substrate 2. The buffer layer 4 is formed of an n-type GaN layer. The first clad layer 6 is formed of an n-type AlGaN/GaN layer. The first waveguide layer 8 is formed of an n-type GaN layer. The active layer 10 is formed of an InGaN MQW(Multi-Quantum Well) layer. The second waveguide layer 12 is formed of a p-type GaN layer. The second clad layer 14 is formed of a p-type AlGaN/GaN layer. The cap layer 16 is formed of a p-type GaN layer. After a photoresist layer (not shown) is formed on the cap layer 16, a photoresist layer pattern 18 is formed by photolithography for forming a ridge structure. The second clad layer 14 is dry-etched to a predetermined depth using the photoresist layer pattern 18 as an etching mask. Then, the photoresist layer pattern 18 is removed, as shown in FIG. 2, and the second clad layer 14 is formed as a ridge structure. Subsequently, as shown in FIG. 3, a passivation layer 22 is formed over the entire surface of the resultant structure after removing the photoresist layer patten 18.
Referring to FIG. 4, after a photoresist layer (not shown) is formed on the passivation layer 22, a photoresist layer pattern 23 is formed for exposing the passivation layer 22 formed on the cap layer 16 by photolithography. The exposed portion of the passivation layer 22 is etched using the photoresist layer pattern 23 as an etching mask. As a result, a via hole 24 for exposing the cap layer 16 is formed. Then, the photoresist layer pattern 23 is removed.
Referring to FIGS. 5 and 6, a p-type electrode 26 is formed on the passivation layer 22 around the via hole 24 in contact with the cap layer 16 (FIG. 5), or a p-type electrode 26a is formed by filling the via hole 24 (FIG. 6).
The passivation layer 22 blocks the flow of current and defines a current path between the p-type electrodes (26, 26a) formed wider than the ridge width and the etched surface, and the ridge width is only a few xcexcm, so that stability and reproducibility of the passivation layer etching process (formation of the via hole 24) is low, the process is complicated, and a process for manufacturing devices becomes long and difficult.
To solve the above problems, it is an objective of the present invention to provide a method for manufacturing a semiconductor laser diode in which a stable p-type electrode is formed, and a passivation layer is formed by a self-alignment method using an etching mask applied to an etching process for forming a ridge structure.
Accordingly, to achieve the above objective, there is provided a method for manufacturing a semiconductor laser diode comprising sequentially forming a buffer layer, a first clad layer, a first waver layer, an active layer, a second waveguide layer, a second clad layer, and a cap layer on a substrate, forming an etching mask on the cap layer, sequentially patterning the cap layer and the second clad layer using the etching mask, and forming a ridge structure by etching the second clad layer in a range of not exposing the active layer, selectively forming a passivation layer for covering the side walls of the cap layer and the second clad layer patterned as the ridge structure using the etching mask, and forming an electrode in contact with the cap layer on the passivation layer when the etching mask is removed.
Preferably, in the above process, the passivation layer is formed by oxidizing the side walls of the ridge structure and the entire exposed surface around the ridge structure, or by directly forming an oxide layer on the side walls of the ridge structure and the entire exposed surface around the ridge structure.
The entire exposed surface around the ridge structure is the entire surface of the second clad layer or the second waveguide layer around the ridge structure.
Preferably, the substrate is a sapphire substrate, a GaN substrate or an SiC substrate.
Preferably, the buffer layer and the first waveguide layer are n-type GaN layers, the first clad layer is an n-type AlGaN/GaN layer, the active layer is an InGaN layer, the second waveguide layer and the cap layer are p-type GaN layers, and the second clad layer is a p-type AlGaN/GaN layer.
Preferably, the etching mask is a photoresist layer, a silicon oxide layer, or a nickel layer.
Preferably, the oxide layer is TiO2, ZrO2, or SiO2.
Preferably, the electrode is formed of a Pd layer.
Also, to achieve the above objective, there is provided a method for manufacturing a semiconductor laser diode comprising sequentially forming a buffer layer, a first clad layer, a first waveguide layer, an active layer, a second waveguide layer, a second clad layer, and a cap layer on a substrate, forming an etching mask on the cap layer, sequentially patterning the cap layer and the second clad layer using the etching mask, and forming a ridge structure by etching the second clad layer in a range of not exposing the active layer, forming a metal layer on the entire surface of the exposed substrate including the ridge structure, in which the cap layer and the second clad layer are sequentially patterned, oxidizing the metal layer, and forming an electrode in contact with the cap layer on the oxide metal layer.
Preferably, in the above process, the metal layer is formed of a Ti layer, a Zr layer, or an Si layer. Also, it is preferable that the metal layer is oxidized by heat-treatment in an oxygen atmosphere.
According to the present invention, a passivation layer is formed by a self-alignment method which does not require photolithography for opening a ridge after forming a passivation layer, which is required in a conventional method for manufacturing a laser diode, so that manufacturing cost and time can be reduced. Also, an electrode can be stably formed on the upper portion of the ridge having a small width, so that reproducibility and productivity of the manufacturing process can be enhanced.